Hydrostatic bearing

ABSTRACT

A hydrostatic bearing in which one of the opposed bearing members has a plurality of part-pockets in it into all of which the hydrostatic fluid is pumped and each of which is surrounded by a ridge. When an impact load is applied to the bearing, the hydrostatic fluid flows out through the gaps between the ridges of the one bearing member and the opposed bearing member into drainage grooves provided in the one bearing member which are disposed between adjacent ridges, and is recirculated.

Waited States Patent [1 1 Gluchowicz Dec. 25, 1973 [5 HYDROSTATHCBEARING 3,597,021 8/1971 Thomas 308/5 R 3,442,560 5 1969 D G [75]Inventor: Gerszon Glucliowicz, Dd ursholm, I 8 ast 308/5 R SwedenFOREIGN PATENTS OR APPLICATIONS Assigneez Bromma Sweden Great Britain R'l [22] F1 ed May 24 1971 Primary Examiner-Charles J. Myhre [21] App].No.: 146,103 Assistant ExaminerR. H. Lazarus Att0rney-Shlesinger,Fitzsimmons & Shlesinger [30] Foreign Application Priority Data May 26,1970 Sweden 7226/70 [57] AB T AC A hydrostatic bearing in which one ofthe opposed [22] 30841751? bearing members has a plurality ofparppockets in it R into all of which the hydrostatic fluid is pumpedand 1 He 0 each of which is surrounded by a ridge. When an impact loadis applied to the bearing, the hydrostatic fluid flows out through thegaps between the ridges of [56] References C'ted the one bearing memberand the opposed bearing UNITED STATES PATENTS member into drainagegrooves provided in the one 2,869,933 1/1959 Bissinger 308/DIG. 1bearing member which are disposed between adjacent 3,484,064 12/1969Koenig 308/5 R ridges, and i8 recirculated 3,476,444 11/1969 Dunfee308/5 R 3,597,020 8/1971 Thomas 308/5 R 2 Claims, 3 Drawing FiguresHYDROSTATKC BEARING BACKGROUND OF THE INVENTION The invention relates toa hydrostatic bearing. Hydrostatic bearings are used in many cases ofrelative movement between machine parts, which cooperate with eachother, such as, e.g., a shaft and a bearing casing or a machine tableand a stand or support. The main advantages with such bearings areelimination of metallic contact and therewith static friction betweenthe machine parts in consideration, production of small friction forcesby movements between said parts and practically total elimination ofwear on the bearing surfaces.

THE PRIOR ART The preponderating type of hydrostatic bearing consists inits simplest shape, in addition to the bearing element proper, of asource of pressure fluid and a throttle member. Of the two surfaces ofthe bearing, one is provided with a plurality of pockets or recesses,which laterally are confined by projections, which in the following willbe called ridges. A device of this type operates principally in such amanner that pressure fluid is pumped into the pockets in the bearingfrom which pressure fluid leaks out through the gaps, which are formedbetween, at one hand, the ridges on the one bearing surface and, at theother hand, the second or opposite bearing surface. After its passagethrough the gaps, the pressure fluid is collected and returned to afluid storage member. The width of the gaps and therewith the throttlingresistance, which they present to the fluid, varies with the spacingbetween the bearing surfaces. The bearing surfaces will automaticallyadapt their spacing from each so that the pressure within each pocket,which is produced by said throttling resistance at every momentcorresponds to the external load on the bearing elements, i.e., in sucha manner that the elements mounted in the bearing are in balance. themaximum pressure in the pocket, which corresponds to the case, when thegap width is equal to zero, is limited to the pump pressure, and thismaximum pump pressure corresponds in turn to a maximum load, which isdetermined by the area of the pocket and the pumping pressure.

The pressure fluid is fed to the individual pocket via a primarythrottling means and the pressure within the pocket will thereby,provided that the pumping pressure does not vary too much, be determinedentirely by the gap width. In many cases the load carrying capacity ofthe bearing is of very great importance. In connection with machinetools, the so-called stiffness is of decisive importance. This stiffnessis generally understood to mean that relative displacement, which isproduced between the bearing surfaces in response to a certain force ora certain load acting on the bearing. The greater force or load isrequired for reducing the gap by a length unit, for example 1 micron,the stiffer the system is and therewith the machine also. This stiffnessis often defined as the static stiffness, which stiffness is determinedby causing a load to act on the machine and by measuring the reductionof the width of the gap after a predetermined period of time. Thedisplacement of the bearing surfaces relative one another, i.e., thereduction of the leakage gap adjacent the pocket, does, however, nottake place in a continuous manner, but with some excess displacement toa minimum gap width during which the pressure in the pocket is built upin such a manner, that the bearing surfaces in response to said pressureare displaced again, but now away from one another into a state ofbalance. This excess movement results in grave problems from the dynamicviewpoint, since the excess movement as such involves great problems inconnection with machine tools. It has been tried to provide staticallystiff bearings by applying regulating systems, which vary the flowpassage area of the throttle member between the pocket and the pump inresponse to an increase of pressure coming into existence, whereby theoutward flow through the gap can rapidly be compensated by increasedflow through the throttle member. However, such regulating systems areexpensive and difficult to construct and result normally in that thedynamic stiffness is impaired.

OBJECTS OF THE INVENTION One main object of the invention is thus toprovide a hydrostatic bearing, which without any regulating systempermits good dynamic rapidity.

SUMMARY OF THE INVENTION According to one main feature of the inventioneach of the individual pressure fluid pockets is subdivided into aplurality of part-pockets having their lateral edges facing one anotherand fed with pressure fluid through associated pressure fluid feederchannels from a pressure fluid supply conduit connected to a throttlemember common to all part pockets, each part-pocket being confined by athrottling ridge cooperating with the opposite bearing surface and adraining groove being provided between adjacent ridge portions of adjoined part-pockets.

BRIEF DESCRIPTION OF THE INVENTION Further objects and advantages of theinvention will become apparent from the following description,considered in connection with the accompanying drawing, which forms partof this specification, and of which FIG. l is a diagrammatic sectionalview of a hydrostatic bearing of known type,

FIG. 2 is a top view of the bearing surface formed with the pocket ofFIG. 1 and FIG. 3 is a simplified top view of a pocket formed inaccordance with the invention.

DETAILED DESCRIPTION OF THE DRAWING FIGURES With reference to thedrawings, FIG. 1 shows a part of a known hydrostatic bearing representedin section. A bearing surface 2, which may be plane or, for example,cylindrical and is formed on a machine bed 1 or a shaft, cooperates witha bearing 3, which has a bearing surface 4 and a pressure fluid pocketor recess 5. This bearing part 3 may be formed on a slide block orcarriage or a similar machine part, which is displaceable in relation tothe bearing surface 2 on the bearing part, or has the shape of a bearingsurrounding a shaft. The pocket 5, which here is shown to be ofrectangular configuration is along its entire circumference confined bya ridge 6 projecting from the bearing surface 4 and having rectangularconfiguration also. Pressure fluid is fed to the pressure fluid pocket 5through a channel 7, which is connected to a conduit 8 provided with athrottle member 9 and connected to a pressure fluid pump not shown inthe drawing.

When pressure fluid is fed to the pocket 5, the pressure in said pocketwill, when the surface 10 of the ridge 6 facing the bearing surface 2bears against said surface, become equal to the output pressure P of thepump. In this way a force is produced between the bearing surface 2 andthe pocket, which is equal to the pressure P multiplied by the area ofthe pocket. Provided that the load force which forces the surface 2against the surface is less than the pressure force within the pocket 5,the bearing part 3 will be lifted away from the part I mounted in thebearing and thereby a throttling gap will be formed between the surface10 and the surface 2 through which gap pressure fluid flows out untilbalance has been established between said forces.

Since the throttle member 9 has a constant passage flow area, thepressure in the pocket will in the position of rest illustrated in FIG.1 be determined by the gap 11 surrounding the pocket, the sole variableof which gap is the gap width h To bring about the required dynamicstiffness, which as already pointed out is of very high importance inconnection with machine tools, the arrangement must be such that when animpact or rapid load acts on the bearing resulting in a reduction of thegap width h the reduction of h must become almost equal to zero, whichin turn implies that the variation of the outflow through the gap 11caused by the reduction of h must be equalized rapidly or totallyavoided. This effect could be obtained by dimensioning the gap widthvery small, e.g., of the order of magnitude of 5 microns, but this wouldnecessitate a finishing working of the bearing surfaces, which is notrealizable in practice, and further require so small gap widths and solittle flow passage area in the throttle member 9 as to expose saidmember to the imminent danger of becoming clogged by impurities in thenormal pressure fluid, oil, or by oil molecules adhering to the walls ofthe throttle passage due to electrostatical charging, which would resultin the flow passage area no longer remaining of constant size.

Thus, with known hydrostatic bearings of the type shown in FIGS. 1 and2, there exists no possibility of bringing about the required dynamicstiffness because firstly the throttle member 9 must have so great aflow passage area that any danger of clogging is avoided, which in turnresults in that secondly for a predetermined circumference of thepocket, the gap width h must be made so great that it becomes impossibleon occurance of an impact to avoid a reduction of the width h of thegap, which has a highly disturbing effect on the operation of machinetools.

This problem is wholly solved by the invention, which renders itpossible to arrange a pocket within the same area of the bearing surfaceas hitherto, but which pocket has a total circumference, which is amultiple of the circumference of the conventional pocket and which thusrenders possible ample flow with a small gap width and with a large flowpassage area in the throttle member 9. The invention is illustrated in asimplified manner in FIG. 3, which shows the bearing surface of thebearing part 3 with the novel pocket. As will be seen from FIG. 3, thepocket 5 of FIG. 2 has been subdivided into a plurality of part-pockets,the number of which is four in the illustrated embodiment and which aredenominated 5a, 5b, Sc and 5d. Each part-pocket,

such as, e.g., the part-pocket 5a, is confined by a ridge 6 of the sametype as shown in FIG. 1, and between adjacent part-pockets, which areshown here to have rectangular configuration with the elongated sidesadjacent each other, a drainage groove 12 is provided, to which groovepressure fluid that streams through the gap portions 11 located adjacenteach other, flows to escape into a collecting receptacle not shown inthe Figure. Each part-pocket is through an associated feeder channel 7a,7b, 7c and 7d, respectively, connected through the conduit 8 to thecommon throttle member 9. Since the pocket shown in FIG. 3 has a totalgap length, which is about 2.5 times greater than the gap length of theembodiment shown in FIGS. 1 and 2, it is easily understood that withunchanged size of the flow passage area of the throttle member 9, thegap width can be reduced considerably without reducing the passage flowand thereby a very rapid replacement of the fluid volume expelledthrough the gaps 11 by an impact load is effected, which in turn resultsin great dynamic stiffness.

By the invention a hydrostatic bearing has thus been provided, in whicheach pocket does not occupy more space than a conventional pocket andwhich in spite thereof allows ample flow of pressure fluid through thethrottle member 9 for the minimum practically realizable gap width hi.e. a hydrostatic bearing processing extremely great dynamic stiffnesswithout any appreciable reduction of the load carrying capacity thereof.

In FIG. 3 only one pocket subdivided into partpockets has beenillustrated. For practical application the bearing part 3 is in amanner, known per se, formed with a plurality of such pockets, namely atleast three and usually four pockets in order to attain requiredbalancing in the journalling of the bearing part.

While one more or less specific embodiment of the invention has beenshown and described, it is to be understood that this is for purpose ofillustration only, and that the invention is not to be limited thereby,but its scope is to be determined by the appended claims.

What is claimed is:

l. A hydrostatic bearing comprising two bearing members mounted forrelative movement therebetween, and with their cooperating bearingportions in opposed relation,

the bearing portion of one of said members having a pocket therein whichis subdivided into and consists of a plurality of pressure fluidpart-pockets separated from one another and each surrounded by aseparating throttle ridge, which cooperates with the bearing portion ofthe other member,

said bearing portion of said one member having drainage grooves thereindisposed between the ridge portions of adjoining part-pockets, and

means connecting said part-pockets to a source of pressure fluid formaintaining said bearing portions in spaced relation with a gaptherebetween during use, comprising a pressure fluid supply conduit,

a plurality of pressure fluid supply ducts con-nected to said supplyconduit and equal in number to said part-pockets, one being connected toeach separate part-pocket, and

a single throttle member disposed in said supply conduit to stabilizethe fluid pressure in all said ducts.

2. A hydrostatic bearing as claimed in claim 1, wherein saidpart-pockets are of equal size and of rectangular configuration in crosssection and are disposed with their elongated lateral sides inparallelism, and said drainage grooves are disposed between the adjacentsides of adjoining part-pockets.

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1. A hydrostatic bearing comprising two bearing members mounted forrelative movement therebetween, and with their cooperating bearingportions in opposed relation, the bearing portion of one of said membershaving a pocket therein which is subdivided into and consists of aplurality of pressure fluid part-pockets separated from one another andeach surrounded by a separating throttle ridge, which cooperates withthe bearing portion of the other member, said bearing portion of saidone member having drainage grooves therein disposed between the ridgeportions of adjoining partpockets, and means connecting saidpart-pockets to a source of pressure fluid for maintaining said bearingportions in spaced relation with a gap therebetween during use,comprising a pressure fluid supply conduit, a plurality of pressurefluid supply ducts con-nected to said supply conduit and equal in numberto said part-pockets, one being connected to each separate part-pocket,and a single throttle member disposed in said supply conduit tostabilize the fluid pressure in all said ducts.
 2. A hydrostatic bearingas claimed in claim 1, wherein said part-pockets are of equal size andof rectangular configuration in cross section and are disposed withtheir elongated lateral sides in parallelism, and said drainage groovesare disposed between the adjacent sides of adjoining part-pockets.